System for determining the dust content of gases

ABSTRACT

A system for measuring the dust content of gases traversing a stack or other duct, e.g., a chimney stack, before release of the gases into the atmosphere, comprises a conduit arrangement with pumps establishing a circulation of air from and to the atmosphere which is unbalanced between the intake and discharge branches to permit induction of the sampled stream of gas from the stack between these branches and upstream of a dust detector. A device for generating an output representing a pressure differential receives one input representing the static pressure of the stack and another input representing the total flow pressure (static pressure + dynamic pressure) therein controls a throttle which, in turn, is followed by an adjustable flowcontrol means for producing the imbalance in accordance with the dynamic pressure of the gases in the stack.

F States Patent 11 91 1451 Jan. 14, 1975 SYSTEM FOR DETERMINING THE DUST CONTENT OF GASES [75] Inventor: Julius Bosch, Rathsberg Bei Erlangen, Germany 22 Filed: Aug. 1, 1973 21 Appl. No.: 384,572

[30] Foreign Application Priority Data Aug. 1, 1972 Germany 2237736 [52] US. Cl 73/28, 55/270, 73/421.5 R [51] Int. Cl. G01n 31/00 [58] Field of Search 73/28, 432 PS, 421.5 R, 73/42l.5 A; 55/27(), 261, 274, 283, DIG. 30, DIG. 41

[56] References Cited UNITED STATES PATENTS 2,901,626 8/1959 Becker 73/421.5 A X 2,930,237 3/1960 Fowle et a1. 73/421.5 A 3,369,346 2/1968 Wildbolz et a1 55/270 X 3,464,257 9/1969 Schreiber et a1 73/28 3,495,463 2/1970 Howell 73/421.5 A 3,501,899 3/1970 Allen 55/270 X FOREIGN PATENTS OR APPLICATIONS 1,156,252 10/1963 Germany 73/28 OTHER PUBLICATIONS Chemical Engineering, Sampling and Analyzing Air Pollution Sources, Morrow et a].., Jan. 24, 1972, pp. 85-98.

Primary ExaminerI-Ierbert Goldstein Assistant ExaminerStephen A. Kreitman Attorney, Agent, or FirmKarl F. Ross; Herbert Dubno [5 7] ABSTRACT A system for measuring the dust content of gases traversing a stack or other duct, e.g., a chimney stack, before release of the gases into the atmosphere, comprises a conduit arrangement with pumps establishing a circulation of air from and to the atmosphere which is unbalanced between the intake and discharge branches to permit induction of the sampled stream of gas from the stack between these branches and upstream of a dust detector. A device for generating an output representing a pressure differential receives one input representing the static pressure of the stack and another input representing the: total flow pressure (static pressure dynamic pressure) therein controls a throttle which, in turn, is followed by an adjustable flow-control means for producing the imbalance in accordance with the dynamic pressure of the gases in the stack.

3 Claims, 1 Drawing lFigure FOR DETERMINING THE DUST SYSTEM CONTENT OF GASES FIELD OF THE INVENTION BACKGROUND OF THE INVENTION Numerous systems have been proposed heretofore for the determination of the particulate content of gas streams conveyed along a duct and, possibly, discharged into the atmosphere. These systems include direct-reading arrangements in which a sensor is provided directly in the stack and monitors the particular compound by combustion or change of any other measurable parameter therein. An analogous system is one which provides a filter across the stack at certain intervals to collect substantially all ofv the particulates whereupon the film is evaluated, e.g., by weighing or by some more detailed analysis.

More recently, it has been desired to provide continuous or intermittent monitoring systems in which a portion of the dust-laden gas is diverted for analysis and accurately represents the remainder of the gas traversing the stack. For this purpose a sampling tube may be provided with a regulator such that the quantity of gas diverted from the stack for analysis (i.e., for determination of the quantity of particulates in the gas of the sample stream) is controllable.

The result obtained with this system is a percentage by weight of the total dust content per unit volume of exhaust gas and, for relatively constant flow velocities over the measurement period, these results are adequate. Difficulties have been encountered when the velocity of gas in the duct varies frequently and sharply within wide ranges. In this case the results obtained are only approximate and the system is disadvantageous from the point of view of environmental pollution. To compensate for the fluctuation by conventional means is expensive and difficult, even where it is possible.

OBJECTS OF THE INVENTION It is the principal object of the present invention to provide an improved system for the monitoring, measurement or detection and sampling of the dust in dustladen gas streams traversing a stack or other duct.

It is another object of the invention to provide a system or device of the character described which is less likely to produce inaccurate results due to fluctuations in the volume rate of flow through the duct to be monitored than earlier systems.

SUMMARY OF THE INVENTION These objects are attained, in accordancewith the present invention, by the use of a two-branch conduit system provided with throttles in the branches so as to establish a flow volume differential between them and thereby induce the sampled portion of the gas to flow into the conduit path, ahead of a particle detector, as a function of the pressure relationships within the stack or duct.

More particularly, the system of the present invention comprises an intake branch having a pump and at least one throttle ahead of this pump (a first throttle), a second branch having a pump and a throttle downstream thereof (a second throttle) for throttling the discharge of the conduit system to the atmosphere by the latter pump, and a particle detector in the conduit network between these pumps, a sampling tube being connected between the stack or duct to be monitored and the conduit means ahead of the particle detector.

According to the invention, a pressure detector (capable of generating an output representing pressure differential) has one side provided with an input for the stack which represents the static pressure therein at the level at which the sampling tube opens into the stack. The other side of the pressure detector receives an input which represents the total flow pressure (static pressure plus dynamic pressure) of the stack so that the pressure detector develops a pressure differential which represents the dynamic pressure in the stack, this pressure being used to control one of these throttles.

Controllers responsive to the flow rates through the two branches are provided and they, consequently, react to the adjustment of the first throttle or the second throttle by the pressure-detecting device to operate an adjustable throttle or other flow-control means in one of the branches in a sense such that the flow rate differential between the branches is minimized or brought to zero as the dynamic pressure in the stack is reduced or brought to zero and vice versa.

While the adjustable first or second throttle may be provided in each branch, I prefer to provide it in the intake branch between its pump and a filter through which the intake branch receives fresh air from the atmosphere. Similarly, while the adjustable throttle may be provided in either branch as will be apparent hereinafter, I prefer to provide it in the intake branch between the variable-cross-section first throttle and the pump of the intake branch.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages will become more readily apparent from the following description, reference being made to the sole FIGURE of the accompanying drawing which is a diagram illustrating the system of the present invention.

SPECIFIC DESCRIPTION In the drawing, 1 show a system for determining the particulate contents of a gas stream traversing a duct and, more specifically, the dust emission from such ducts as chimneys, smokestacks and industrial gas discharge facilities.

The system, for the smokestack 1, comprises an intake suction tube (intake branch) 2 provided with a filter 3 and an adjustable throttle (first throttle) 4. The setting positioning throttle or flow-control means 5 is provided downstream of the throttle 4 in the form of a flap of the butterfly type while a suction pump 6 is connected downstream of the butterfly throttle 5 to induce gas through the filter.

At the output side of the pump 6, a duct 7 is provided in communication with a duct 8 to the input 9 of a dustmeasuring device or dust detector 9, 10, II which, for the sake of simplicity, has been shown as a filter band 10. The dust in the gases traversing this filter band is collected on the latter and is measured, e.g., by weighing or some other means such as the blocking of a light beam, and converted into a weight or volume or particle-number measure per unit of time. A device of this type has been shown at 1 and described in German Pat. No. 2,032,172 (see also the English language reprint RECORDING COUNTER FOR THE CONTINUOUS DETERMINATION OF THE CONCENTRATION OF PULVERULENT AIR POLLUTANTS, STAUB REIN- HALTUNG DER LUFT, Vol. 27 (1967) No. 10, pp. 21-24).

At the outlet 11 of the dust-measuring device, there is provided a duct (outlet branch) 12 having a throttle (second throttle) 13 of fixed cross-section which is spanned by tubes 16 and 17 connected to opposite chambers of a pneumatic bellows 15. The pneumatic bellows is coupled with a pneumatic bellows 14 whose inlets 18 and 19 are bridged to opposite sides of the throttle 4. The pneumatic bellows 15 may comprise a membrane 15a in a housing 15b subdivided into a compartment 15c receiving the higher pressure from line 16 and a compartment 15d receiving the lower pressure from the downstream side of the throttle 13 via tube 14.

The membrane is connected at l5e with a rod pivotally connected at 20a with the butterfly valve 5.

The bellows 14 is provided with a membrane 14a connected at 14:: to the rod 20 and received withing a housing 14b subdivided into the low-pressure compartment 14c and the high-pressure compartment 14d by the membrane. Compartment 140 is connected by tube 18 to the line 2 downstream of the throttle 4 while compartment 14d is connected by line 19 to this conduit upstream of the throttle 4.

The pressure differential at the throttles 4 and 13 thus serves to operate the bellows 14, 15, together forming a unit whose output is the rod 20 connected to the positioning throttle 5 as previously described.

A sampling tube 21 (running at least initially parallel to the stack axes) is connected to the duct system previously described between the output of pump 6 and the input 9 of the dust-measuring device 9, 11), 11, and extends into the chimney or stack 1 to terminate in a plane 23 perpendicular to the axis of the stack and at which the mouth of tube 21 opens in a direction opposite that of gas flow through the stack.

A pump 22 is provided between the output side 11 of the dust-measuring device and the throttle 13 and drives air through the latter toward an outlet 112a communicating with the atmosphere. The pumps 6 and 22 are driven by a common motor 23.

At the level of the horizontal measuring plane of stack 1, there are provided further intake openings 24 and 25. The intake opening 24 serves to sense the static pressure in the stack 1 while opening 25 responds to the total pressure (dynamic or flow pressure plus static pressure) in the stack. Opening 24 of the stackpressure sensing means is connected by a duct 26 with one compartment 27a of a pressure-sensing capsule 27 having a membrane 27b subdividing the capsule 27 into the compartment 27a and a further compartment 27c. The latter communicates via line 28 with the opening 25 of the differential-pressure sensing means.

As described for the bellows 14 and 15, the capsule 27 contains the membrane which provides an output in the form of a linear displacement which is proportional to the pressure differential across the membrane. The membrane 27b is connected to a tension spring 29. The

membranes of the pressure-detecting capsules 27, and the bellows l4 and 15 and the throttle 5 have a median position which has been shown in the drawing. A rod 30 connects the membrane 27b of the pressuredetecting devise 27 with the throttle 4 in such manner as to control the effective cross-section of the constriction formed thereby. In its open position, the throttle 4 has substantially the same cross-section as the throttle 13.

When the gas flow velocity through the stack 1 of smoke or other particulate-containing gases is zero the spring 29 draws the membrane of the pressuredetecting device 27 into its extreme left-hand position and imposes the larges cross-section of throttle 4 in the conduit 2. The membranes in the bellows 14 and 15 assume such positions that the throttle 5 is opened and the pump 6 draws fresh air through filter 3 from the atmosphere, as mentioned, via duct 2 while air is returned to the atmosphere by pump 22 and outlet conduit 12. The system is pneumatically balanced so that substantially no partial stream of gas is withdrawn from the stack 1 by the sampling tube 21.

When the stack gases traversing the chimney l have some speed, the pressure detector 27 responds to proportionally reduce the cross-section of throttle 4. More particularly, the total pressure detected at 25 applied to one side of the membrane is greater than the static pressure detected at 24 and applied to the other side of the membrane, the pressure differential displacing the membrane 27b against the force of the tension spring 29.

The pressure differential is a measurement of the dynamic pressure in stack 1, and rod 30 thereby proportionally reduces the cross-section of the throttle and hence the velocity with which the fresh air traverses intake conduit 2. The pressure differential across the throttle thereby increases and is converted into a pressure differential at bellows 14 which shifts the rod 20 upwardly and effectively reduces the cross-section of throttle 5 until the pressure differential at the throttle 4 again reaches its original velocity. A large quantity of fresh air is thus drawn in through duct 2 by comparison with the quantity of gas-laden air displaced by the pump 22 and discharged through duct 12. This flowquantity differential requires replacement by induction of gas through the sampling tube 21 from the stack. Consequently, as the flow velocity in stack 1 increases, the dynamic pressure and the quantity of sampling gas increases.

The spring 29 is of adjustable tension as represented by the arrow 29a so that its force can be set with respect to the characteristics of throttle 4, bellows l4, bellows l5 and throttle Ssuch that the withdrawal velocity of the gas in sampling tube 21 corresponds to the gas flow velocity in the remaining cross-section of the stack 1. In this manner an equivelocity of isokinetic withdrawal of the sampled gas is ensured. The spring 29 allows, moreover, temperature compensation in a simple way since the equivelocity arrangement ensures that the same proportion of the sampled gas will be withdrawn with high stack temperatures as with low stack temperatures.

Of course, the adjustable throttles 4 and 5 need not be provided in the intake line 2 only but one or more of these throttles can also be disposed in the discharge line 12. Thus the throttle 4 controlled by the pressuredetecting device can be provided in the intake line 2 while the throttle 5 controlled by the regulator 14 and 15 can be provided in line 12 although, whereas the system illustrated in the drawing requires a decreased crosssection for throttle 5, the alternative system will provide an increased cross-section. Furthermore, instead of the throttle 4 the throttle 13 may be made adjustable by the pressure-detecting device 27 and in this case the throttle 13 must be its smallest cross-section when the flow velocity in the intake is zero. Finally, it is possible to provide an arrangement whereby throttle 5 remains in the intake line 2 and throttle 4 has a fixed cross-section while throttle 13 is adjustable by the device 27.

I claim:

1. A system for measuring the dust content of a gas stream traversing a duct, said system comprising:

a pair of motor-driven pumps, each having an inlet and an outlet, the inlet of one of said pumps and the outlet of the other pump forming respective branches communicating with the atmosphere;

a dust detector having an input side connected to the outlet of said one of said pumps and an output side connected to the inlet of said other pump;

a sampling tube open into said duct and communicating with said input side of said dust detector down stream of said one of said pumps;

a first hrottle located at said inlet branch downstream of its communication with the atmosphere and a second throttle located at said outlet branch upstream of its communication with the atmosphere;

means for varying the effective flow cross section of one of said throttles;

operating means responsive to the flow velocity of said gas stream in said duct and operatively connected to said means for varying said cross section for adjusting said cross section of said one of said throttles to generate a flow-rate differential between said inlet branch and said outlet branch in dependence upon said flow velocity; and an automatic differential controller including:

an adjustable-cross section further throttle in one of said branches,

a control member shiftable in response to a pressure differential across said branches, and

means operatively connecting said control member to said first throttle for increasing the flow-rate differential across said branches in conjunction with said operating means upon an increase in said flow velocity and vice versa.

2. The system defined in claim 1 wherein said operating means includes:

a pressure-sensing capsule responsive to pressures applied to opposite sides thereof for producing an output representing the differential of the latter pressures;

means for applying the static pressure in said duct to one side of said pressure-sensing capsule; and

means for applying the total velocity pressure in said duct to the other side of said pressure-sensing capsule.

3. The system defined in claim .2 wherein said automatic differential controller further comprises respective pneumatic bellows having tubes bridged on opposite sides of said first and second throttles in said inlet and outlet branches. 

1. A system for measuring the dust content of a gas stream traversing a duct, said system comprising: a pair of motor-driven pumps, each having an inlet and an outlet, the inlet of one of said pumps and the outlet of the other pump forming respEctive branches communicating with the atmosphere; a dust detector having an input side connected to the outlet of said one of said pumps and an output side connected to the inlet of said other pump; a sampling tube open into said duct and communicating with said input side of said dust detector downstream of said one of said pumps; a first hrottle located at said inlet branch downstream of its communication with the atmosphere and a second throttle located at said outlet branch upstream of its communication with the atmosphere; means for varying the effective flow cross section of one of said throttles; operating means responsive to the flow velocity of said gas stream in said duct and operatively connected to said means for varying said cross section for adjusting said cross section of said one of said throttles to generate a flow-rate differential between said inlet branch and said outlet branch in dependence upon said flow velocity; and an automatic differential controller including: an adjustable-cross section further throttle in one of said branches, a control member shiftable in response to a pressure differential across said branches, and means operatively connecting said control member to said first throttle for increasing the flow-rate differential across said branches in conjunction with said operating means upon an increase in said flow velocity and vice versa.
 2. The system defined in claim 1 wherein said operating means includes: a pressure-sensing capsule responsive to pressures applied to opposite sides thereof for producing an output representing the differential of the latter pressures; means for applying the static pressure in said duct to one side of said pressure-sensing capsule; and means for applying the total velocity pressure in said duct to the other side of said pressure-sensing capsule.
 3. The system defined in claim 2 wherein said automatic differential controller further comprises respective pneumatic bellows having tubes bridged on opposite sides of said first and second throttles in said inlet and outlet branches. 